I'm about half-way through the fantasy novel Sabriel, and the heroine happens to be tall and slender. Initially I thought -why are heroes of books and movies nearly always tall?
Traditionally, heroes are always tall (slender if female, athletic if male).
So it's nice to come across short heroes. Buffy (of BTVS fame) is, of course, always referred to as short. She's probably average height for a woman, and her lack of lankiness is always exagerated by the presence of tall male characters such as Angel and Riley. But then, that's all part of the whole idea of having as the Slayer someone who looks like a good victim i.e. small and delicate.
Then there're the hobbits. It would've been too easy for Aragorn, or Legolas to be the main heroes. But it's the halflings who save the world, eh?
Mini-me, from the Austen Powers movie, was evil, so he doesn't count.
Children don't count, because they're supposed to be short, and anyway it's only until they grow up.
I can't think of any others. Can you?